In order to understand how animal development is controlled by gene expression we must discover the rules which allow the developmental regulation of genes. Towards this end we are studying 3 gene sets which are expressed sequentially in the larval and prepupal salivary glands of Drosophila melanogaster and whose regulation is dependent on the steroid hormone 20-OH ecdysone. Our long-term goals are to discover 1) the mechanisms involved which allow coordinate expression of member genes of a gene set, 2) how the products of the primary hormone-responding gene set autoregulate their own expression and activate the expression of the tissue-specific secondary hormone-responding gene set and 3) how a general hormone signal (which probably reaches all cells in the larva) is able to initiate many different tissue-specific gene responses. We plan to study a small to initiate many different tissue-specific gene responses. We plan to study a small number of member genes of each gene set using recombinant DNA and molecular biological techniques in order to describe their a) structural organization at the DNA level, b) transcriptional programs at the developmental and tissue level, c) gene products and d) relatedness to one another in terms of hypothetical regulatory domains at the DNA level. In addition we plan a molecular analysis of several previously described mutants which potentially code for an interesting transcriptional regulatory factor.